Low-cost alloyed Q460C / D steel plate and production method thereof
By optimizing alloying elements and process design, the problems of high production cost and difficulty in balancing performance of Q460C/D steel plates have been solved, realizing the production of alloyed Q460C/D steel plates with low cost, high strength and good toughness, thus meeting market demand.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-21
- Publication Date
- 2026-03-27
AI Technical Summary
In the existing technology, the production cost of Q460C/D steel plate is relatively high, and it is difficult to balance high strength and low temperature impact toughness, resulting in a very narrow controllable range of process, which makes it difficult to meet the market's demand for low-cost and economical products.
By optimizing the addition of alloying elements, especially controlling the content of elements such as carbon, manganese, and chromium, and combining this with reasonable smelting, rolling, and heat treatment processes, we can ensure that the strength and toughness of the steel plate meet the technical requirements, while controlling production costs.
We have achieved the production of low-cost alloyed Q460C/D steel plates, which possess high strength and good low-temperature impact toughness, meeting market demands. Furthermore, through grain refinement and rational process design, we have ensured the controllability and economy of the production process.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of heavy plate production, specifically involving a low-cost alloyed Q460C / D steel plate and its production method. Background Technology
[0002] In recent years, with the steady growth of the engineering industry and the deepening of global applied technology research, the Q460C / D has been increasingly widely used, especially in engineering machinery and construction, where it has demonstrated its strong vitality. However, with increased production and changes in the economic situation, the problem of higher costs has arisen, making the market demand for low-cost and economical alternatives increasingly urgent. Summary of the Invention
[0003] To solve the aforementioned problems, the inventors, through repeated theoretical calculations and continuous experimentation, obtained a low-cost alloyed Q460C / D steel plate. This steel plate has a cost advantage and addresses the urgent market demand.
[0004] Another object of the present invention is to provide a low-cost method for producing alloyed Q460C / D steel plates.
[0005] To achieve the above objectives, the technical solution adopted by this invention is: a low-cost alloyed Q460C / D steel plate with a thickness of ≤80mm, comprising the following chemical composition by mass percentage: C: 0.06~0.08, Si: 0.1~0.3, Mn: 1.50~1.60, P≤0.010, S≤0.003, Als: 0.025~0.035, Nb: 0.020~0.030, Ti: 0.008-0.015, with the remainder being Fe and residual elements, Ceq≤0.35, while controlling the carbon equivalent (Ceq=C+Mn / 6+Si / 24+Ni / 40+Cr / 5+Mo / 4+V / 14).
[0006] Steel plates require high strength performance, and the product requires steel plates to possess both high strength and good low-temperature impact toughness. The biggest challenge these two contradictory technical requirements pose to process design is the extremely narrow controllable range of the process. Alloying elements need to be added to ensure this, optimizing alloying elements such as Nb and V without reducing strength and toughness, to guarantee that all performance indicators meet the technical requirements. As can be seen from the properties of steel, carbon is also an important alloying element. It can increase the strength and hardness of steel, but it has an adverse effect on toughness. The carbon content in steel determines the temperature regime for smelting, rolling, and heat treatment. Carbon can significantly change the liquid and solidification properties of steel. At 1600℃, when [C]≤0.8%, for every 0.1% increase in carbon, the melting point of steel decreases by 6.50℃, the density decreases by 4 kg / m³, and the viscosity decreases by 0.7%. Manganese is a very weak deoxidizer. At very low carbon content and high oxygen content, it can exhibit a deoxidizing effect, assisting in deoxidation and improving its deoxidizing capacity. Manganese can slightly increase the strength of steel and improve its hardenability, stabilizing and expanding the austenite region. Mn can increase the stability of austenite and expand the γ-phase region to obtain austenite. It lowers the critical cooling rate during quenching. The critical points (A1 and A3) of steel are lowered by 25-30°C compared to carbon steels of the same carbon content, thus improving hardenability and reducing deformation during quenching, making it suitable for thick plates. Among all carbides, chromium carbides are the finest, distributing evenly throughout the steel volume, resulting in high strength, hardness, yield point, and wear resistance. Because it refines and evenly distributes the microstructure, it also provides good plasticity and toughness, which is particularly valuable for tool steels. Composition design is the foundation for ensuring performance. It combines the comprehensive effects of basic elements such as C, Si, Mn, and Al in the chemical composition on improving the strength and affecting the ductility and toughness of steel, as well as the harmful effects of P and S on high-strength alloy steels. In order to give full play to the dual effects of solid solution strengthening and grain refinement strengthening, the steel plate's various performance indicators meet or exceed the standard requirements without reducing ductility and toughness, while ensuring the most economical production cost.
[0007] The above-mentioned low-cost alloyed Q460C / D steel plate production method includes the following steps: 1) KR molten iron pretreatment: The molten iron arriving at the station must have both front and rear slag removed to ensure that the slag layer thickness on the liquid surface is ≤30mm. After KR stirring and desulfurization, the molten iron S is guaranteed to be ≤0.005%, the desulfurization cycle is guaranteed to be ≤25min, and the desulfurization temperature drop is guaranteed to be ≤25℃. 2) Smelting and casting: VD arrives at the station at 1668℃, pre-evacuates to vacuum for 5 minutes, holds pressure for 20 minutes to break the vacuum, and then blows softly for 5 minutes before leaving the station at 1586℃. The hydrogen concentration is 0.79ppm, which meets the standard. It is required that the holding time be ≥20 minutes under a vacuum of 67Pa, and that the molten steel turbulence effect be good during the holding process. The VD leaving the station temperature is 1570~1575℃. 3) Heating: Following the principle of fully heating the billet, the homogenization temperature is selected as 30~50℃ above the equilibrium temperature of the alloy for full solid solution. The billet heating temperature is 1180~1230℃, and the heating time is calculated according to the billet thickness at 1min / mm. 4) High-temperature recrystallization direct rolling: The rolling temperature in the recrystallization zone is above 980℃, and the thickness to be heated is 2.2 to 2.5 times the thickness of the finished product; the second-stage rolling temperature is 800-830℃, and the single-pass reduction rate in the second stage is guaranteed to be ≥15%, and the cumulative reduction rate is ≥60%; the final rolling temperature is 790-810℃. After rolling, DQ+ACC cooling is used, the cooling rate is controlled at 10-20℃ / s, and the outlet water temperature is controlled at 370-400℃.
[0008] Impurities in molten steel, including sulfur (S), phosphorus (P), and various oxide inclusions, tend to segregate significantly during solidification, greatly impacting the mechanical properties and metallurgical quality of extra-thick plates. Achieving good internal quality and ensuring compliance with Class I flaw detection standards is fundamentally achieved through clean steel smelting, primarily ensured through two aspects: firstly, the total level of non-metallic inclusions in the molten steel must be below 3.0; secondly, the content of the five major harmful elements in the molten steel must be strictly controlled. LF ladle refining involves fine-tuning the composition, argon stirring, foamed slag submerged arc heating, and reducing atmosphere white slag. The VD (Vacuum Deposition) temperature is 1668℃ upon arrival, pre-evacuated to vacuum for 5 minutes, held for 20 minutes to break the vacuum, and soft-blown for 5 minutes before leaving the station at 1586℃. The hydrogen concentration is 0.79 ppm, meeting the standard. The requirement is a vacuum of 67 Pa and a holding time of ≥20 minutes, with good turbulence during the holding process. The VD departure temperature is 1570~1575℃.
[0009] Establish a reasonable heating regime: A reasonable billet heating regime can ensure that the alloy second phase particles are fully dissolved during the heating process, and also ensure that the austenite grains do not coarsen.
[0010] The complete solution temperature of Nb in the steel billet is 1150℃. High-temperature laser experiments were conducted to observe the change in the original austenite content with temperature in a 150mm steel plate. The austenite grain size changes at different heating temperatures show that when the heating temperature increases from 1100℃ to 1180℃, the original austenite grain size remains below 60 μm; however, when the heating temperature increases to 1250℃, the original austenite grains begin to merge and grow unevenly, reaching a grain size of 100 μm, indicating coarsening. Following the principle of sufficient heating of the steel billet, a homogenization temperature of 30-50℃ above the equilibrium temperature for complete alloy solution was selected as the homogenization temperature. Therefore, the steel billet heating temperature was chosen to be 1180-1230℃, and the heating time was calculated at 1 min / mm.
[0011] High-temperature recrystallization direct rolling technology: Achieving sufficient fragmentation of the core grain structure and maximum defect fusion in a limited number of rolling passes is key to the rolling technology of Q460C / D steel plates. Due to the low compression ratio, a one-stage recrystallization zone rolling process is used for extra-thick steel plates, allowing for sufficient recrystallization at high temperatures and refining the austenite grains. Calculations show that the austenite recrystallization termination temperature of the billet is controlled above 1000℃. Based on the relationship between austenite grain size and deformation per rolling pass, a recrystallization rolling temperature of 1050~1100℃ is selected. To achieve sufficient fragmentation of the core grain structure and maximum defect fusion in the billet, it is essential to ensure that rolling deformation is effectively transferred to the core of the extra-thick steel plate. The allocation of rolling passes for extra-thick steel plates strives to ensure sufficient deformation of the core structure during the rolling process. During the rolling process, the reduction rate increases sequentially with each pass, achieving a deformation of 17% reduction in a single pass. Afterward, to ensure proper sheet shape, the reduction rate gradually decreases. Strict control of rolling force and torque is maintained during rolling, ensuring a rolling force of over 8600 tons and a rolling torque of over 3200 kNm. Simultaneously, bending roll force adjustment is strengthened to regulate sheet shape.
[0012] According to Tarnovsky's research, the shape factor l / h of the deformation zone is directly related to the deformation amount per rolling pass. When the shape factor l / h > 0.5, the compressive deformation penetrates completely into the workpiece, resulting in a phenomenon where the deformation in the central layer is greater than that on the surface. Conversely, when the shape factor l / h < 0.5, as the shape factor decreases, the compressive deformation cannot penetrate into the workpiece and remains limited to the vicinity of the surface layer. Based on Tarnovsky's rolling deformation theory, the deformation in each pass can penetrate to the core of the steel plate, maximizing the improvement of the core microstructure under the premise of a small compression ratio. Immediately after final rolling, the steel plate undergoes strong water cooling to retain the refined austenite microstructure to the maximum extent, preventing grain growth and achieving the goal of grain refinement.
[0013] Controlled rolling process for refining austenite grains: Among the factors that improve the strength and toughness of steel plates, grain refinement contributes significantly to both. In the rolling process of Q460C / D steel plates, recrystallization rolling technology and non-recrystallization rolling technology are fully utilized to refine the austenite grains of the rolled steel plate. Based on the relationship curve between the austenite recrystallization termination temperature and the elemental solid solution content for grain refinement, the rolling temperature in the recrystallization zone was determined to be above 980℃. The higher the rolling temperature, the greater the deformation per pass, and the finer the austenite grain size. Therefore, given a fixed composition system and rolling temperature, effectively increasing the reduction rate per pass in the recrystallization zone, especially the total reduction rate in the longitudinal rolling stage after steel transfer, becomes crucial for fully refining the austenite recrystallized grains. Maintaining the rolling deformation in the non-recrystallization zone allows for the acquisition of fully flattened deformed austenite, accumulating deformation and dislocations, creating more nucleation sites, and promoting the acquisition of a fine phase transformation structure after phase transformation. Increasing the reduction rate during the longitudinal rolling stage, especially after the steel transfer stage, significantly improves the core toughness. While considering the finished steel plate size, the billet size should be optimized as much as possible, using wide billet rolling to reduce the number of widening passes and increasing the number of rolling passes and deformation in the recrystallization zone. In the granular bainite microstructure obtained after strong water cooling, small, dispersed M / A islands remain on the bainitic ferrite matrix, as well as M / A islands at the boundaries of granular clusters or quasi-polygonal ferrite. Detailed Implementation
[0014] To better describe the technical features of the present invention, an example is provided to demonstrate the production of a low-cost alloyed Q460C / D steel plate, achieved through the following production method: 1) The composition design is as follows: chemical composition by mass percentage (unit, wt%): C: 0.06~0.08, Si: 0.1~0.3, Mn: 1.50~1.60, P≤0.010, S≤0.003, Als: 0.025~0.035, Nb: 0.020~0.030, Ti: 0.008-0.015, the others are Fe and residual elements, Ceq≤0.35, and the carbon equivalent is controlled (Ceq=C+Mn / 6+Si / 24+Ni / 40+Cr / 5+Mo / 4+V / 14).
[0015] 2) KR molten iron pretreatment process: The molten iron arriving at the station must have both the front slag and the rear slag removed to ensure that the slag layer thickness on the liquid surface is ≤30mm. After KR stirring and desulfurization, the molten iron S is guaranteed to be ≤0.005%, the desulfurization cycle is guaranteed to be ≤25min, and the desulfurization temperature drop is guaranteed to be ≤25℃.
[0016] 3) Smelting and casting process: VD arrives at 1668℃, pre-evacuates to vacuum for 5 minutes, holds pressure for 20 minutes to break the vacuum, soft blows for 5 minutes, and leaves the station at 1586℃. The hydrogen concentration is 0.79ppm, meeting the standard. The requirement is to hold pressure for ≥20 minutes at a vacuum of 67Pa, while ensuring good turbulence of the molten steel during the pressure holding process. VD departure temperature: 1570~1575℃.
[0017] 4) Heating process: Following the principle of fully heating the billet, the homogenization temperature is selected as 30~50℃ above the equilibrium temperature of the alloy for full solidification. Therefore, the billet heating temperature is selected as 1180~1230℃, and the heating time is calculated at 1min / mm.
[0018] 5) High-temperature recrystallization direct rolling technology: Based on the relationship curve between the austenite recrystallization termination temperature and the elemental solid solution content for grain refinement, the rolling temperature in the recrystallization zone was determined to be above 980℃. The thickness at the pre-crystallization stage is 2.2 to 2.5 times the finished product thickness, laying the foundation for the cumulative deformation, grain refinement, and dislocation strengthening in the finishing rolling stage. The second-stage initial rolling temperature is 800-830℃, and the single-pass reduction rate in the second stage is guaranteed to be ≥15%, and the cumulative reduction rate is ≥60%. This ensures that deformation penetration flattens and elongates the austenite grains, increases the effective area of grain boundaries, and effectively forms a large number of deformation bands, providing more nucleation points for austenite phase transformation, thereby achieving the purpose of refining austenite grains. The final rolling temperature is 790-810℃. After rolling, DQ+ACC cooling is used, with the cooling rate controlled at 10-20℃ / s, and the outlet water temperature controlled at 370-400℃.
[0019] Table 1 illustrates the physical properties of 80mm Q460D steel plates:
[0020] The steel plate produced by the above method has a thickness of 80mm.
Claims
1. A low-cost alloyed Q460C / D steel plate, characterized in that: The steel plate thickness is ≤80mm, and includes the following chemical composition by mass percentage: C: 0.06~0.08, Si: 0.1~0.3, Mn: 1.50~1.60, P≤0.010, S≤0.003, Als: 0.025~0.035, Nb: 0.020~0.030, Ti: 0.008-0.015, with the remainder being Fe and residual elements, Ceq≤0.35, while controlling the carbon equivalent (Ceq=C+Mn / 6+Si / 24+Ni / 40+Cr / 5+Mo / 4+V / 14).
2. The method for producing low-cost alloyed Q460C / D steel plate according to claim 1, characterized in that: Includes the following steps: 1) KR molten iron pretreatment: The molten iron arriving at the station must have both front and rear slag removed to ensure that the slag layer thickness on the liquid surface is ≤30mm. After KR stirring and desulfurization, the molten iron S is guaranteed to be ≤0.005%, the desulfurization cycle is guaranteed to be ≤25min, and the desulfurization temperature drop is guaranteed to be ≤25℃. 2) Smelting and casting: VD arrives at the station at 1668℃, pre-evacuates to vacuum for 5 minutes, holds pressure for 20 minutes to break the vacuum, and then blows softly for 5 minutes before leaving the station at 1586℃. The hydrogen concentration is 0.79ppm, which meets the standard. It is required that the holding time be ≥20 minutes under a vacuum of 67Pa, and that the molten steel turbulence effect be good during the holding process. The VD leaving the station temperature is 1570~1575℃. 3) Heating: Following the principle of fully heating the billet, the homogenization temperature is selected as 30~50℃ above the equilibrium temperature of the alloy for full solid solution. The billet heating temperature is 1180~1230℃, and the heating time is calculated according to the billet thickness at 1min / mm. 4) High-temperature recrystallization direct rolling: The rolling temperature in the recrystallization zone is above 980℃, and the thickness to be heated is 2.2 to 2.5 times the thickness of the finished product; the second-stage rolling temperature is 800-830℃, and the single-pass reduction rate in the second stage is guaranteed to be ≥15%, and the cumulative reduction rate is ≥60%; the final rolling temperature is 790-810℃. After rolling, DQ+ACC cooling is used, the cooling rate is controlled at 10-20℃ / s, and the outlet water temperature is controlled at 370-400℃.